1. Field of the Invention
The present invention relates to electro-optic wave guides and more particularly to an electro-optic wave guide for both intensity/modulating and deflecting an incident light beam which might typically be a laser beam.
2. Prior Art
Scanning systems which utilize laser beams for transmitting information are known. U.S. Pat. No. 3,848,087, for example, entitled "Optical Scanner Control System" discloses a scanning system which utilizes a multifaceted mirror for deflecting a light beam over a scanning area. As successive mirror facets rotate into the path of an incident light beam the beam repetitively sweeps across the scanning area. Systems which utilize apparatus such as that disclosed in the '087 Patent have applications in both raster input scanning (RIS) and in raster output scanning (ROS). In raster input scanning, the light beam illuminates an original document line by line and enables the information contained in that document to be encoded through procedures known in the art.
For raster output scanning, the moving light beam may be used to encode information onto an information carrying media, such as a charged photoreceptor, a scanning system must encode information into the light beam and also must distribute that information across the photoreceptor. To accomplish the encoding of information prior art ROS systems typically intensity modulate the light beam at controlled intervals. As the beam scans the photoreceptor, the modulation dictates which areas will remain charged and which areas will discharge.
As raster output scanning has evolved certain refinements have been made in the encoding technique. One such refinement involves facet tracking of the intensity modulated beam. It should be appreciated that when a light beam is fixed and is caused to impinge upon a rotating mirror, the light beam traverses each facet of the multi-faceted mirror. Experience with prior art scanning systems indicates that the movement of the light beam across a facet of the mirror reduces the effectiveness of the scanning system. It is more efficient if the light beam follows or tracks a center of a particular facet as that facet moves in relation to the light beam. Consequently, errors introduced by inhomogeneity in the facet are largely eliminated. To provide this so called facet tracking the light beam must be deflected in space before it contacts the spinning mirror facet. These two ROS requirements of intensity modulating and deflecting are at present satisfied by bulk acousto-optic modulator devices. Such modulating devices are known in the art and are commercially available but are relatively costly and experience has shown that they are effective only over a limited optical wavelength.
To overcome these disadvantages in acousto-optic modulating devices, proposals have been made to utilize electro-optic modulators to replace the acousto-optic device. One such proposal is disclosed in U.S. Pat. No. 4,047,795 to Hughes et al. The Hughes et al. Patent recognizes the possibility of deflecting an incoming laser beam using an optical integrated circuit which includes control electrodes for deflecting the beam in a controlled manner. While addressing the deflection requirement of a conventional laser scanning system, the Hughes et al. patent does not deal with the intensity modulation requirement of a raster output scanning system. Indeed, applicant knows no raster scanning system which utilizes an integrated wave guide device for providing both intensity modulation and beam deflection on a single substrate. Thus, although in theory the Hughes et al. deflection technique could be combined with known methods of intensity modulating a laser beam, such a combination would require a separate beam modulator which would have to be optically coupled to the deflection device disclosed in the '795 Patent.
A further problem with use of an electro-optic wave guide crystal as an in-line device for ROS systems is the potential for optically damaging the wave guide by passing the high power laser beams required through its wave guide portion. Applicant knows of no prior art fabrication technique, for example, for producing an electro-optic wave guide having sufficient resistance to optical damage for extended time periods as required in a raster output scanning application.